import math

class ParticipationAdoptionIndex:
    
    def __init__(self, num_participants, target_population, feedback_volume):
        self.num_participants = num_participants
        self.target_population = target_population
        self.feedback_volume = feedback_volume
        self.components_1 = {}
        self.components_2 = {}

    # ---------- helper function(s) ---------- 
    def _compute_pci(self, participants_by_group):
        total = sum(participants_by_group.values())
        if total == 0:
            return 0.0

        shares = [
            count / total
            for count in participants_by_group.values()
        ]

        return sum(s ** 2 for s in shares)
            
    # ---------- public API ----------
    def compute_pai(self, participants_by_group=None):

        # input validation for 'participants_by_group'
        self.num_participants = sum(participants_by_group.values()) if participants_by_group else num_participants
        
        # absolute counts
        spi_a_abs = self.target_population - self.num_participants
        spi_b_abs = self.num_participants - self.feedback_volume

        # ----- 'Participation Dynamics' components -----
        pcr = self.num_participants / self.target_population
        spi_a = spi_a_abs / self.target_population
        spi_b = spi_b_abs / self.num_participants
        peg = spi_b_abs / self.target_population
        
        # ----- 'Reach and Equity' components -----
        pci = self._compute_pci(participants_by_group) if participants_by_group else 0.0
        effective_groups = 1.0 / pci if pci > 0 else 0.0
        effective_groups_int = int(math.floor(effective_groups))
        effective_groups_rounded = int(round(effective_groups))

        # ----- percent-based values -----
        final_pcr = round(pcr * 100, 2)
        final_spi_a = round(spi_a * 100, 2)
        final_spi_b = round(spi_b * 100, 2)
        final_peg = round((pcr - peg) / pcr * 100 if pcr > 0 else 0.0, 2)
        final_pci = round(pci, 2)

        # ----- pci pivot value -----
        pci_mid = 0.5
        # ---------------------------
        
        self.components_1 = {
            "PCR (Participation Coverage Ratio)": {"Value": final_pcr, "Description": f"{final_pcr}% of the target population have participated."},
            "SPI-A (Silent Participation Inference - Silent Non-Adoption)": {"Value": final_spi_a, "Description": f"{final_spi_a}% of the target population were not reached or excluded."},
            "SPI-B (Silent Participation Inference - Silent Adoption)": {"Value": final_spi_b, "Description": f"{final_spi_b}% of the participants have participated silently."},
            "PEG (Participation-to-Expression Gap)": {"Value": final_peg, "Description": f"There is a {final_peg}% gap between participation and expressed feedback."}
        }

        self.components_2 = {
            "PCI (Participation Concentration Index)": 
                {"Value": final_pci, 
                 "Description": (
                    f"A PCI of {final_pci} suggests "
                    f"{'high' if final_pci >= pci_mid else 'low'} participation concentration, "
                    f"{'dominated by fewer groups' if final_pci >= pci_mid else 'with participation spread across groups'}."
                )},
            "Group Summary": 
                {"Minimum Participating Groups": f"At least {effective_groups_int} groups meaningfully participated.", 
                 "Effective Participation Groups": f"Participation is roughly equivalent to {effective_groups_rounded} equally sized groups."
                }
        }

        return self.components_1, self.components_2