# Claro Standard Library: csv (RFC4180-ish)
# Use: IMPORT "lib/csv.claro" AS csv
# read(text, sep)  -> LIST of rows (each row is LIST of fields)
# write(rows, sep) -> TEXT (quotes fields when needed)
#
# Supports:
# - quoted fields: "a,b"
# - escaped quotes inside quoted fields: ""
# - newlines inside quoted fields
EXPORT ALL

TEACH _needs_quote TAKES field, sep
    FIND sep IN field AS p1
    FIND "\"\n\"" IN field AS p2
    FIND "\""\r\"" IN field AS p3
    FIND "\""\"\"" IN field AS p4
    IF (p1 != 0) OR (p2 != 0) OR (p3 != 0) OR (p4 != 0)
        RETURN YES
    ENDIF
    RETURN NO
LEARNED

TEACH _escape_quotes TAKES field
    # Replace " with ""
    SET out TO ""
    LENGTH field AS L
    FOR i FROM 1 TO L
        SUBSTR field FROM i LEN 1 AS ch
        IF ch = "\""\"\"" 
            SET out TO out + "\""\"\"" + "\""\"\"" 
        ELSE
            SET out TO out + ch
        ENDIF
    DONE
    RETURN out
LEARNED

TEACH write TAKES rows, sep
    SET out TO ""
    FOR EACH row IN rows
        SET line TO ""
        SET first TO YES
        FOR EACH field IN row
            SET f TO field
            CALL _needs_quote WITH f, sep
            IF RESULT = YES
                CALL _escape_quotes WITH f
                SET f TO "\""\"\"" + RESULT + "\""\"\"" 
            ENDIF

            IF first = YES
                SET line TO f
                SET first TO NO
            ELSE
                SET line TO line + sep + f
            ENDIF
        DONE
        SET out TO out + line + "\n"
    DONE
    RETURN out
LEARNED

TEACH read TAKES text, sep
    # State machine CSV parser
    SET rows TO LIST
    SET row TO LIST
    SET cur TO ""
    SET inq TO NO

    LENGTH text AS L
    FOR i FROM 1 TO L
        SUBSTR text FROM i LEN 1 AS ch

        IF inq = YES
            IF ch = "\""\"\"" 
                # quote or escaped quote?
                IF i < L
                    SUBSTR text FROM (i + 1) LEN 1 AS nx
                    IF nx = "\""\"\"" 
                        SET cur TO cur + "\""\"\"" 
                        SET i TO (i + 1)
                    ELSE
                        SET inq TO NO
                    ENDIF
                ELSE
                    SET inq TO NO
                ENDIF
            ELSE
                SET cur TO cur + ch
            ENDIF
        ELSE
            IF ch = "\""\"\"" 
                SET inq TO YES
            ELSE
                IF ch = sep
                    ADD cur TO row
                    SET cur TO ""
                ELSE
                    IF ch = "\n"
                        ADD cur TO row
                        ADD row TO rows
                        SET row TO LIST
                        SET cur TO ""
                    ELSE
                        IF ch != "\r"
                            SET cur TO cur + ch
                        ENDIF
                    ENDIF
                ENDIF
            ENDIF
        ENDIF
    DONE

    # final field / row
    ADD cur TO row
    # avoid adding a trailing empty row from final newline
    IF (L > 0)
        ADD row TO rows
    ENDIF
    RETURN rows
LEARNED