path.f90

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!> @file
!! @defgroup group_path Path
!! A modern, portable Fortran module for path manipulation and basic directory operations.
!! This module provides a clean interface for working with file system paths
!! in a platform-independent way. It correctly handles both Unix ('/') and Windows ('\') path
!! separators through conditional compilation and offers deferred-length character results
!! for maximum flexibility.
!!
!! The module builds upon the @link fpx_string fpx_string @endlink module for @link fpx_string::string string @endlink type support
!! and provides
!! overloads of key procedures to accept either intrinsic `character(*)` or `type(string)`
!! arguments.
!!
!! Features
!! - Detection of absolute and rooted paths on Windows and Unix-like systems
!! - Safe path joining that avoids duplicate separators
!! - Extraction of directory part, filename (with or without extension)
!! - Path splitting into head/tail components
!! - Retrieval of the current working directory (`cwd`)
!! - Changing the current working directory (`chdir`)
!!
!! @note All path-returning functions return allocatable deferred-length characters.
!! @note The public generic `join` interface works with any combination of `character` and `string`.
!!
!! @section path_examples Examples
!! @code{.f90}
!! character(:), allocatable :: p1, p2, full
!!
!! p1 = '/home/user/docs'
!! p2 = 'report.pdf'
!! full = join(p1, p2)                ! => '/home/user/docs/report.pdf'
!!
!! print *, is_absolute(full)         ! .true.  (on Unix)
!! print *, filename(full)            ! 'report'
!! print *, filename(full,.true.)     ! 'report.pdf'
!! print *, dirpath(full)             ! '/home/user/docs'
!! ...
!! @endcode
!!
!! On Windows:
!! @code{.f90}
!! character(:), allocatable :: p
!! p = join('C:\Users', 'Alice', 'Documents')
!! ! p == 'C:\Users\Alice\Documents'
!! print *, is_absolute(p)   ! .true.
!! ...
!! @endcode
module fpx_path
    use, intrinsic :: iso_c_binding
    use fpx_string
 
    ! allow(default-public-accessibility)
    implicit none; public
 
    !! @cond
#ifdef _WIN32
    character, parameter    :: separator = '\'
    character(*), parameter :: alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
#else
    character, parameter :: separator = '/'
#endif
 
#ifdef _WIN32
    interface
        function getcwd_c(buf, size) bind(C, name='_getcwd') result(r)
            import
            implicit none
            type(c_ptr) :: r
            ! allow(assumed-size, assumed-size-character-intent)
            character(kind=c_char), intent(out) :: buf(*)
            integer(kind=c_size_t), value       :: size
        end function
    end interface
#else
    interface
        function getcwd_c(buf, size) bind(C, name='getcwd') result(r)
            import
            implicit none
            type(c_ptr) :: r
            ! allow(assumed-size, assumed-size-character-intent)
            character(kind=c_char), intent(out) :: buf(*)
            integer(kind=c_size_t), value       :: size
        end function
    end interface
#endif
 
    interface
        integer(c_int) function chdir_c(path) bind(C, name='chdir')
            import
            implicit none
            ! allow(assumed-size)
            character(kind=c_char), intent(in) :: path(*)
        end function
    end interface
    !! @endcond
 
    !> Generic interface for joining two path components
    !! Supports all combinations of character and string arguments
    !!
    !! @b Remarks
    !! @ingroup group_path
    interface join
        module procedure :: join_character_character
        module procedure :: join_string_character
        module procedure :: join_character_string
        module procedure :: join_string_string
    end interface
 
contains
 
    !> Returns .true. if the path is absolute.
    !! On Unix a path is absolute when it starts with '/'.
    !! On Windows a path is absolute when it starts with a drive letter followed by ':\'
    !! (e.g. 'C:\', 'd:/temp').
    !!
    !! @param[in] filepath  Path to test
    !! @return res          .true. if filepath is absolute
    !!
    !! @code{.f90}
    !!    print *, is_absolute('/home/user')   ! .true.  (Unix)
    !!    print *, is_absolute('C:\\Temp')     ! .true.  (Windows)
    !!    print *, is_absolute('docs/..')      ! .false.
    !!    ...
    !! @endcode
    !!
    !! @b Remarks
    !! @ingroup group_path
    pure logical function is_absolute(filepath) result(res)
        character(*), intent(in)        :: filepath
#ifdef _WIN32
        if (len(filepath) < 2) then
            res = .false.
            return
        end if
        res = scan(filepath(1:1), alphabet) /= 0 .and. filepath(2:2) == ':'
#else
        res = filepath(1:1) == separator
#endif
 
    end function
 
    !> Returns .true. if the path is rooted (starts with a separator) or is absolute.
    !! A rooted path begins with the platform separator ('\' on Windows, '/' elsewhere)
    !! even if it is not a full absolute path (e.g. '/temp' on Linux).
    !!
    !! @param[in] filepath  Path to test
    !! @return res          .true. if filepath is rooted
    !!
    !! @b Remarks
    !! @ingroup group_path
    pure logical function is_rooted(filepath) result(res)
        character(*), intent(in)        :: filepath
        !private
        integer :: length
 
        length = len(filepath)
#ifdef _WIN32
        res = (length >= 1 .and. filepath(1:1) == separator) .or. is_absolute(filepath)
#else
        res = (length > 0 .and. filepath(1:1) == separator)
#endif
    end function
 
    !> Extracts the filename part of a path.
    !! By default the extension is stripped. If keepext=.true. the full filename
    !! including extension is returned.
    !!
    !! @param[in] filepath   Full or relative path
    !! @param[in] keepext    Optional; keep extension when .true.
    !! @return res           Filename (without path)
    !!
    !! @code{.90}
    !!    print *, filename('dir/file.txt')        ! 'file'
    !!    print *, filename('dir/file.txt',.true.) ! 'file.txt'
    !!    print *, filename('archive.tar.gz')      ! 'archive.tar'
    !! @endcode
    !!
    !! @b Remarks
    !! @ingroup group_path
    pure function filename(filepath, keepext) result(res)
        character(*), intent(in)        :: filepath
        character(:), allocatable       :: res
        logical, intent(in), optional   :: keepext
        !private
        integer :: ipoint, islash
 
        ipoint = index(filepath, '.', back=.true.)
        islash = index(filepath, separator, back=.true.)
        if (ipoint < islash) ipoint = len_trim(filepath) + 1
        if (present(keepext)) then
            if (keepext) then
                res = filepath(islash + 1:len_trim(filepath))
            else
                res = filepath(islash + 1: ipoint - 1)
            end if
        else
            res = filepath(islash + 1: ipoint - 1)
        end if
    end function
 
    !> Joins two path components with the correct platform separator.
    !! Removes duplicate separators and trailing/leading whitespace.
    !!
    !! @param[in] path1  First path component
    !! @param[in] path2  Second path component
    !! @return res       Joined path
    !!
    !! @b Remarks
    pure function join_character_character(path1, path2) result(res)
        character(*), intent(in) :: path1
        character(*), intent(in) :: path2
        character(:), allocatable :: res
        !private
        character(:), allocatable :: temp
 
        temp = trim(adjustl(path1))
        if (temp(len(temp):len(temp)) == separator) temp = trim(temp(:len(temp) - 1))
 
        res = temp // separator // trim(adjustl(path2))
    end function
 
    !> Joins character path with string path component.
    !! Removes duplicate separators and trailing/leading whitespace.
    !!
    !! @param[in] path1  First path component
    !! @param[in] path2  Second path component
    !! @return res       Joined path
    !!
    !! @b Remarks
    pure function join_character_string(path1, path2) result(res)
        character(*), intent(in) :: path1
        type(string), intent(in) :: path2
        character(:), allocatable :: res
        !private
        character(:), allocatable :: temp
 
        temp = trim(adjustl(path1))
        if (temp(len(temp):len(temp)) == separator) temp = trim(temp(:len(temp) - 1))
 
        res = temp // separator // trim(adjustl(path2%chars))
    end function
 
    !> Joins string path with character path component.
    !! Removes duplicate separators and trailing/leading whitespace.
    !!
    !! @param[in] path1  First path component
    !! @param[in] path2  Second path component
    !! @return res       Joined path
    !!
    !! @b Remarks
    pure function join_string_character(path1, path2) result(res)
        type(string), intent(in) :: path1
        character(*), intent(in) :: path2
        character(:), allocatable :: res
        !private
        character(:), allocatable :: temp
 
        temp = trim(adjustl(path1%chars))
        if (temp(len(temp):len(temp)) == separator) temp = trim(temp(:len(temp) - 1))
 
        res = temp // separator // trim(adjustl(path2))
    end function
 
    !> Joins two string path components.
    !! Removes duplicate separators and trailing/leading whitespace.
    !!
    !! @param[in] path1  First path component
    !! @param[in] path2  Second path component
    !! @return res       Joined path
    !!
    !! @b Remarks
    pure function join_string_string(path1, path2) result(res)
        type(string), intent(in) :: path1
        type(string), intent(in) :: path2
        character(:), allocatable :: res
        !private
        character(:), allocatable :: temp
 
        temp = trim(adjustl(path1%chars))
        if (temp(len(temp):len(temp)) == separator) temp = trim(temp(:len(temp) - 1))
 
        res = temp // separator // trim(adjustl(path2%chars))
    end function
 
    !> Returns the directory part of a path (everything before the last separator).
    !! @param[in] filepath  Path to analyse
    !! @return res          Directory component
    !!
    !! @code {.f90}
    !!    print *, dirpath('/home/user/file.txt')  ! '/home/user'
    !! @endcode
    !!
    !! @b Remarks
    !! @ingroup group_path
    pure function dirpath(filepath) result(res)
        character(*), intent(in) :: filepath
        character(:), allocatable :: res
        !private
        character(:), allocatable :: temp
 
        call split_path(filepath, res, temp)
    end function
 
    !> Returns the base name (filename) part of a path.
    !! @param[in] filepath  Path to analyse
    !! @return res          Base name component
    !!
    !! @code{.f90}
    !!    print *, dirname('/home/user/file.txt')  ! 'file.txt'
    !! @endcode
    !!
    !! @b Remarks
    !! @ingroup group_path
    pure function dirname(filepath) result(res)
        character(*), intent(in) :: filepath
        character(:), allocatable :: res
        !private
        character(:), allocatable :: temp
 
        call split_path(filepath, temp, res)
    end function
 
    !> Splits a path into head (directory) and tail (basename) components.
    !! @param[in]  filepath  Input path
    !! @param[out] head      Directory part (includes trailing separator when appropriate)
    !! @param[out] tail      Base name part
    !!
    !! @b Remarks
    !! @ingroup group_path
    pure subroutine split_path(filepath, head, tail)
        character(*), intent(in)                :: filepath
        character(:), allocatable, intent(out)  :: head
        character(:), allocatable, intent(out)  :: tail
        !private
        character(:), allocatable :: temp
        integer :: i, ipoint, isep
 
        ! Empty string, return (.,'')
        if (len_trim(filepath) == 0) then
            head = '.'; tail = ''
            return
        end if
 
        ! Remove trailing path separators
        temp = trim(adjustl(filepath))
        if (temp(len(temp):len(temp)) == separator) then
            temp = trim(temp(:len(temp) - 1))
        else
            ipoint = index(filepath, '.', back=.true.)
            isep = index(filepath, separator, back=.true.)
            if (ipoint > isep .and. isep > 0) then
                temp = trim(temp(:isep - 1))
            end if
        end if
 
        if (len_trim(temp) == 0) then
            head = separator
            tail = ''
            return
        end if
 
        i = len(temp) - index(temp, separator, back=.true.) + 1
 
        ! if no `pathsep`, then it probably was a root dir like `C:\`
        if (i == 0) then
            head = temp // separator
            tail = ''
            return
        end if
 
        head = temp(:len(temp) - i)
 
        ! child of a root directory
        if (index(temp, separator, back=.true.) == 0) then
            head = head // separator
        end if
 
        tail = temp(len(temp) - i + 2:)
    end subroutine
 
    !> Returns the current working directory as a deferred-length character string.
    !! Returns empty string on failure.
    !!
    !! @return res  Current working directory
    !! @code{.f90}
    !!    character(:), allocatable :: here
    !!    here = cwd()
    !!    print *, 'We are in: ', here
    !! @endcode
    !!
    !! @b Remarks
    !! @ingroup group_path
    function cwd() result(res)
        character(:), allocatable :: res
        !private
        character(len=1, kind=c_char) :: buf(256)
        integer :: i, n
        integer(c_size_t) :: s
 
        s = size(buf, kind=c_size_t)
        if (c_associated(getcwd_c(buf, s))) then
            n = findloc(buf, achar(0), 1)
            allocate(character(n - 1) :: res)
            do i = 1, n - 1
                res(i:i) = buf(i)
            end do
        else
            res = ''
        end if
    end function
 
    !> Changes the current working directory.
    !! @param[in]  path  Directory to change to
    !! @param[out] err   Optional integer error code (0 = success, non-zero = failure)
    !! @code{.f90}
    !!    integer :: ierr
    !!    call chdir('/tmp', ierr)
    !!    if (ierr /= 0) stop 'Failed to change directory'
    !! @endcode
    !!
    !! @b Remarks
    !! @ingroup group_path
    subroutine chdir(path, err)
        character(*), intent(in)        :: path
        integer, optional, intent(out)  :: err
        integer :: loc_err
 
        loc_err = chdir_c(path // c_null_char)
 
        if (present(err)) err = loc_err
    end subroutine
end module