--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/validate_fasta.py	Thu Mar 03 02:54:20 2022 +0000
@@ -0,0 +1,177 @@
+"""Validate input FASTA sequence."""
+
+import re
+import argparse
+from typing import List, TextIO
+
+
+class Fasta:
+    def __init__(self, header_str: str, seq_str: str):
+        self.header = header_str
+        self.aa_seq = seq_str
+
+
+class FastaLoader:
+    def __init__(self, fasta_path: str):
+        """Initialize from FASTA file."""
+        self.fastas = []
+        self.load(fasta_path)
+        print("Loaded FASTA sequences:")
+        for f in self.fastas:
+            print(f.header)
+            print(f.aa_seq)
+
+    def load(self, fasta_path: str):
+        """Load bare or FASTA formatted sequence."""
+        with open(fasta_path, 'r') as f:
+            self.content = f.read()
+
+        if "__cn__" in self.content:
+            # Pasted content with escaped characters
+            self.newline = '__cn__'
+            self.caret = '__gt__'
+        else:
+            # Uploaded file with normal content
+            self.newline = '\n'
+            self.caret = '>'
+
+        self.lines = self.content.split(self.newline)
+        header, sequence = self.interpret_first_line()
+
+        i = 0
+        while i < len(self.lines):
+            line = self.lines[i]
+            if line.startswith(self.caret):
+                self.update_fastas(header, sequence)
+                header = '>' + self.strip_header(line)
+                sequence = ''
+            else:
+                sequence += line.strip('\n ')
+            i += 1
+
+        # after reading whole file, header & sequence buffers might be full
+        self.update_fastas(header, sequence)
+
+    def interpret_first_line(self):
+        line = self.lines[0]
+        if line.startswith(self.caret):
+            header = '>' + self.strip_header(line)
+            return header, ''
+        else:
+            return '', line
+
+    def strip_header(self, line):
+        """Strip characters escaped with underscores from pasted text."""
+        return re.sub(r'\_\_.{2}\_\_', '', line).strip('>')
+
+    def update_fastas(self, header: str, sequence: str):
+        # if we have a sequence
+        if sequence:
+            # create generic header if not exists
+            if not header:
+                fasta_count = len(self.fastas)
+                header = f'>sequence_{fasta_count}'
+
+            # Create new Fasta
+            self.fastas.append(Fasta(header, sequence))
+
+
+class FastaValidator:
+    def __init__(self, fasta_list: List[Fasta]):
+        self.fasta_list = fasta_list
+        self.min_length = 30
+        self.max_length = 2000
+        self.iupac_characters = {
+            'A', 'B', 'C', 'D', 'E', 'F', 'G',
+            'H', 'I', 'K', 'L', 'M', 'N', 'P',
+            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
+            'Y', 'Z', '-'
+        }
+
+    def validate(self):
+        """performs fasta validation"""
+        self.validate_num_seqs()
+        self.validate_length()
+        self.validate_alphabet()
+        # not checking for 'X' nucleotides at the moment.
+        # alphafold can throw an error if it doesn't like it.
+        #self.validate_x()
+
+    def validate_num_seqs(self) -> None:
+        if len(self.fasta_list) > 1:
+            raise Exception(f'Error encountered validating fasta: More than 1 sequence detected ({len(self.fasta_list)}). Please use single fasta sequence as input')
+        elif len(self.fasta_list) == 0:
+            raise Exception(f'Error encountered validating fasta: input file has no fasta sequences')
+
+    def validate_length(self):
+        """Confirms whether sequence length is valid. """
+        fasta = self.fasta_list[0]
+        if len(fasta.aa_seq) < self.min_length:
+            raise Exception(f'Error encountered validating fasta: Sequence too short ({len(fasta.aa_seq)}aa). Must be > 30aa')
+        if len(fasta.aa_seq) > self.max_length:
+            raise Exception(f'Error encountered validating fasta: Sequence too long ({len(fasta.aa_seq)}aa). Must be < 2000aa')
+
+    def validate_alphabet(self):
+        """
+        Confirms whether the sequence conforms to IUPAC codes.
+        If not, reports the offending character and its position.
+        """
+        fasta = self.fasta_list[0]
+        for i, char in enumerate(fasta.aa_seq.upper()):
+            if char not in self.iupac_characters:
+                raise Exception(f'Error encountered validating fasta: Invalid amino acid found at pos {i}: "{char}"')
+
+    def validate_x(self):
+        """checks if any bases are X. TODO check whether alphafold accepts X bases. """
+        fasta = self.fasta_list[0]
+        for i, char in enumerate(fasta.aa_seq.upper()):
+            if char == 'X':
+                raise Exception(f'Error encountered validating fasta: Unsupported aa code "X" found at pos {i}')
+
+
+class FastaWriter:
+    def __init__(self) -> None:
+        self.outfile = 'alphafold.fasta'
+        self.formatted_line_len = 60
+
+    def write(self, fasta: Fasta):
+        with open(self.outfile, 'w') as fp:
+            header = fasta.header
+            seq = self.format_sequence(fasta.aa_seq)
+            fp.write(header + '\n')
+            fp.write(seq + '\n')
+
+    def format_sequence(self, aa_seq: str):
+        formatted_seq = ''
+        for i in range(0, len(aa_seq), self.formatted_line_len):
+            formatted_seq += aa_seq[i: i + self.formatted_line_len] + '\n'
+        return formatted_seq
+
+
+def main():
+    # load fasta file
+    args = parse_args()
+    fas = FastaLoader(args.input_fasta)
+
+    # validate
+    fv = FastaValidator(fas.fastas)
+    fv.validate()
+
+    # write cleaned version
+    fw = FastaWriter()
+    fw.write(fas.fastas[0])
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "input_fasta",
+        help="input fasta file",
+        type=str
+    )
+    return parser.parse_args()
+
+
+
+if __name__ == '__main__':
+    main()