"""Bridging the gap: one English sentence, three defensible programs.

Backs the "Bridging the Gap" frames in Latex/FrameLibrary/L1L2Review.tex.
The request is "Show me the common words in this file". Nothing in that
sentence fixes what a word is, or what common means. Each reading below is a
faithful implementation of the same sentence, and each returns a different
answer.

Run: python3 bridging_the_gap.py

Install:  nothing, the Python standard library is enough
"""

import re
from collections import Counter

TEXT = "The cat sat on the mat. The Cat did not sit on the dog."

STOPWORDS = {"the", "on", "did", "not", "a", "an", "and", "of", "to", "is"}


def reading_a(text):
    """Word means whatever whitespace separates. Common means most frequent."""
    return Counter(text.split())


def reading_b(text):
    """Word means letters only, case folded. Common means most frequent."""
    return Counter(re.findall(r"[a-z]+", text.lower()))


def reading_c(text):
    """Reading B, minus the words that carry no topic."""
    counts = reading_b(text)
    return Counter({w: c for w, c in counts.items() if w not in STOPWORDS})


def top(counts, k=3):
    """Rank by count, break ties alphabetically so the answer is repeatable."""
    return sorted(counts.items(), key=lambda kv: (-kv[1], kv[0]))[:k]


def rank_of(counts, word):
    order = sorted(counts.items(), key=lambda kv: (-kv[1], kv[0]))
    for i, (w, _) in enumerate(order, start=1):
        if w == word:
            return i
    return None


def show(name, counts):
    print(f"\n{name}")
    print(f"  token count : {sum(counts.values())}")
    print(f"  vocabulary  : {len(counts)}")
    print(f"  top 3       : {top(counts)}")
    print(f"  full        : {top(counts, k=len(counts))}")


if __name__ == "__main__":
    print(f"input: {TEXT}")

    a = reading_a(TEXT)
    b = reading_b(TEXT)
    c = reading_c(TEXT)

    show("Reading A  split on spaces, keep case, keep punctuation", a)
    show("Reading B  lower case, letters only", b)
    show("Reading C  reading B without stop words", c)

    print("\nWhere does 'cat' land?")
    for name, counts in (("A", a), ("B", b), ("C", c)):
        hits = counts.get("cat", 0)
        print(f"  reading {name}: count {hits}, rank {rank_of(counts, 'cat')}")

    print("\nTokens produced by reading A:")
    print(" ", TEXT.split())
    print("Tokens produced by reading B:")
    print(" ", re.findall(r"[a-z]+", TEXT.lower()))